Within the field of the techniques of printed circuit manufacturing, there are many cases when it is necessary to position an artwork with respect to the plate of a printed circuit for insolation purposes.
This is particularly the case for the insolation step so as to define with photoetching the strip conductors of the printed circuit. The corresponding installation is used to expose to ultraviolet rays, during a given time, the printed circuits covered with a film or a photosensitive resist through an artwork mounted on a mobile support to insolate the corresponding part of the photosensitive resist or film defined by the artwork.
It is clear that a fundamental point of this operation consists in the accuracy of the artwork positioning with respect to the printed circuit on which insolation will be carried out. The artwork is arranged on a horizontal support which is usually made up of a rectangular metal frame on which a glass is fixed, the artwork being arranged on the glass in order to allow for insolation. In the particular case of the invention, the supporting device concerns the case where the artwork is moved be positioned accurately with respect to the flat piece and especially with respect to the printed circuit plate.
In the great majority of this type of machines, the ultra-violet exposure is used for only one side of the printed circuit plate. In this case, the machine has only one support for the artwork which is a lower support. However, when the printed circuit plate is of the double-sided type which is more and more common, the use of machines allowing to simultaneously insolate the printed circuit through two artworks is particularly interesting. Such machines have been proposed, in particular in U.S. Pat. No. 5,337,151 and in European patent application EP 618 505. In such machines, because of the presence of two artworks, it is thus necessary to provide two artwork supports arranged on either side of the printed plate circuit.
Independently of the number of artwork supports among the solutions proposed until now, the artwork support has a certain weight, especially because of the presence of the glass supporting the artwork and the frame weight which must be very rigid, the displacements are obtained by means of two devices usually called tables, each device enabling to move the support in a direction X or in the directions X and Y that are orthogonal with each other. These tables support mechanically the whole support and must thus be at the same time a displacement device in a horizontal plane and a mechanical support in the vertical direction. This means that the motor(s) must have a significant power in case the displacement follows two axes. Moreover, considering the accuracy of the positioning that is desired, the weight and therefore the inertia of the whole support to be moved cause the displacements to be very slow, even though they are very limited, which requires a rather important time period for positioning a support and thus an artwork with respect to the reference piece, that is to say about several tens of seconds.
In the case of an installation, for example to insolate the printed circuit from artworks arranged on the support which operates with an automatic supply of printed circuits, the necessary time to position the support very substantially reduces the operating rate of the whole installation.
This way, there is a real need of artwork support devices which can be moved very accurately but in a reduced time period compared with the currently known solutions.
It is an object of the present invention to provide an artwork support device and more particularly, means for moving this support which make it possible to reduce the time necessary for the final positioning phase while keeping the same accurate positioning.